1. Technical Field
The present invention relates to a liquid jet apparatus and printing apparatus arranged to print predetermined letters and images by emitting microscopic droplets of liquids from a plurality of nozzles to form the microscopic particles (dots) thereof on a printing medium.
2. Related Art
An inkjet printer as one of such printing apparatuses, which is generally low-price and easily provides high quality color prints, has widely spread not only to offices but also to general users along with the widespread of personal computers and digital cameras.
In recent inkjet printers, printing in fine tone is required. Tone denotes a state of density of each color included in a pixel expressed by a liquid dot, the size of the dot corresponding to the color density of each pixel is called a tone grade, and the number of the tone grades capable of being expressed by a liquid dot is called a tone number. Fine tone denotes that the tone number is large. In order to change the tone grade, it is required to modify a drive pulse to an actuator provided to a liquid jet head. In the case in which a piezoelectric element is used as the actuator, since the amount of displacement of the piezoelectric element (distortion of a diaphragm, to be precise) becomes large when the voltage value applied to the piezoelectric element becomes large, the tone grade of the liquid dot can be changed very accurately.
Therefore, in JP-A-2003-1824, a plurality of drive pulses with different wave heights are combined and joined, the drive pulses are commonly output to the piezoelectric elements of the nozzles of the same color provided to the liquid jet head, a drive pulse corresponding to the tone grade of the liquid dot to be formed is selected for every nozzle out of the plurality of drive pulses, the selected drive pulses are supplied to the piezoelectric elements of the corresponding nozzles to emit droplets of the liquid different in amount, thereby achieving the required tone grade of the liquid dot.
However, there is a problem that the waveform of the drive pulse is distorted by the parasitic inductance, the parasitic capacitance, and the resistance of the wiring of the drive circuit, and the capacitance of the actuator, such as a piezoelectric element, and moreover, the amount of the waveform distortion varies in accordance with the number of actuators, such as piezoelectric elements, driven by the drive pulse. The waveform distortion of the drive pulse leads to variation in the amount of the liquid, causing variation in the size of the liquid dot, thus leading to degradation of the print quality. It should be noted that the variation in the amount of the liquid also depends on the individual difference of the nozzle or the actuator. Further, in the case in which a plurality of drive pulses is combined in chronological order and joined to each other, the drive pulse corresponding to the tone grade of a liquid dot to be formed is selected for every nozzle from the plurality of drive pulses, and the selected drive pulse is applied to the actuator of the corresponding nozzle, there is caused a shift in the liquid jet emission timing between the nozzles of the actuators for which the different drive pulses are selected, thus the liquid dot forming (or landing) positions vary and cause degradation of the print quality.